The invention relates to sensor assemblies, and more particularly to speed-sensor assemblies.
Sensor assemblies, and more particularly speed-sensor assemblies are commonly used in a wide range of applications ranging from automotive anti-lock brake and transmission systems to various automated manufacturing and conveyor lines. In an anti-lock brake system, for example, a speed-sensor assembly is positioned adjacent a wheel of a vehicle to monitor the speed at which the wheel is rotating. When the sensor assembly determines that the brakes have been applied to stop the rotation of the wheel, the anti-lock brake system engages to rapidly pulse the brakes and stop the vehicle in a controlled manner. The speed-sensor assemblies associated with anti-lock brake systems can be used in tire deflation detection systems that monitor the speed of wheel rotation to determine whether a tire on the wheel is likely to be deflated.
Sensor assemblies use sensing devices that can be characterized as either active or passive sensing devices. An active sensing device is one that requires a power source to function. A passive sensing device does not require power. One known form of an active speed-sensing device that is used in conjunction with anti-lock brake systems is a magneto-resistive sensing device. A magneto-resistive sensing device has a predetermined magnetic field associated therewith. When placed adjacent the teeth of a gear or other similar component of the wheel assembly, the magnetic field is interrupted by the passing of each gear tooth, thereby changing the resistance in the sensing device. As a current is passed through the sensing device, the changes in resistance associated with the changes in the magnetic field vary the current flow through the sensing device. By monitoring the current flow through the sensing device, it is possible to determine the speed at which the wheel is rotating.
Another type of active sensing device commonly used in anti-lock brake applications utilizes the Hall Effect. A Hall-Effect sensing device also has a predetermined magnetic field associated therewith and is also mounted adjacent a toothed gear. As the teeth pass by the sensing device, the magnetic field of the sensing device is interrupted. The variation in the magnetic field creates a variation in the voltage measured across the sensing device. The voltage can be monitored to determine the speed at which the wheel is rotating.
Regardless of the specific type used, the active sensing device is typically packaged in a sensor assembly that includes the sensor device itself and a connector terminal that can be coupled to a power supply. The sensor assembly also may include a capacitor that is coupled to both the sensing device and the connector terminal. As is commonly understood by those of skill in the art, the capacitor helps reduce electrical interference or noise that might otherwise diminish the effectiveness of the sensing device (some devices have self-contained conditioning circuits and do not require an additional capacitor). The components of the sensor assembly are welded, soldered, or crimped together to create the mechanical and electrical connections needed (crimping is accomplished with a pre-formed crimp bucket on the terminal connector). Heretofore, welding, soldering, and crimping with a crimp bucket have been the only means employed to effect these mechanical and electrical connections.
There are several potential failure modes and processing issues with the prior art sensor assemblies. The sensor assemblies described above, and particularly those used for automotive applications, are typically produced in large quantities. It is therefore desirable to assemble the sensor assemblies in an efficient, reliable, and cost-effective manner. It has been found that the commonly-practiced resistance welding, crimping, and soldering processes are not robust enough or have excessive tooling/component costs for creating the numerous electrical and mechanical connections required on each sensor assembly. Because the sensing components and terminals are small or have intricate geometry, welding, crimping, or soldering the sensor terminals and capacitor to the connector terminal is a very constrained, time-consuming, and difficult process. Each welded, crimped, or soldered connection must be produced individually. This can involve four or more welds, crimps, or solder joints in an extremely small area.
Multiple connections in a process often result in improperly-formed connections (more joints equals increased probability of failure). The weld characteristics are extremely position-sensitive, meaning that the quality of the connection will vary significantly depending upon the relative position of the components being welded. Air gaps between the welded terminals can degrade the quality of the welded connections, thereby affecting the reliability of the sensing device. Welding or soldering also exposes the sensing device and the sensing device housing to high localized heat that can damage or destroy the sensing device and the housing. Welding and soldering require on-going maintenance to keep the process running properly.
Crimping with a fixed crimp bucket can lead to stresses that can damage the sensing device. Improper crimps due to improper component alignment can create poor connections to the sensing device, which in turn, can create defective products.
These problems necessitate expensive quality control measures. Each welded or soldered connection must be visually inspected using an automated vision system to insure the quality of the connection. Terminals with crimp buckets must be precisely designed to create proper retention force. Terminals with crimp buckets must be monitored with crimp force monitors to assure the process is correct. Due in large part to these inadequate welding, soldering, and crimping operations, the volume of sensor assemblies that are rejected as being deficient in some respect is high compared to the volume of sensor assemblies produced.
Other design features are also complicated in light of the welding, crimping, and soldering processes. For example, the connector terminal to which the sensor terminals and the capacitor terminals are welded or soldered must be electroplated with tin or other conductive materials to improve the conductive bond. Electroplating each connector terminal adds cost to the sensor assembly. Additionally, the connector terminal must be enlarged and perhaps even specially configured to accommodate the welding or soldering. For use in a crimping application, the connector terminal must have adequate space between each lead to allow the crimp bucket to be formed during the stamping process. These requirements increase the size and cost of the entire sensor assembly.
The present invention recognizes these and other problems with the prior art sensor assemblies, and provides an improved sensor assembly and method for manufacturing the same. The sensor assembly of the present invention is formed without the troublesome welding, crimping, or soldering operations. Instead, splice bands are used to create multiple mechanical and electrical xe2x80x9csplice connectionsxe2x80x9d in a single junction in a quick and reliable manner. As a result, the number of connection points required is reduced and thus the number of deficient and defective sensor assemblies is reduced. The cost of assembly, terminal tooling, and quality control testing is also reduced. Furthermore, the design and manufacture of the connector terminal is greatly simplified, and the overall size of the sensor assembly can potentially be reduced.
The spliced connections are preferably in the form of separate, free-floating splice bands that are cut from a strip of conductive material, formed into U-shaped forms, placed over the various terminals to be coupled, pressed closed to surround the terminals, and then crimped to secure the bands in place. These splice bands are well-suited for the tight space constraints associated with the sensor assembly and can be easily adjusted for changes in part geometry. Compared to a terminal with a crimp bucket that requires a unique terminal for each part design, the spliced joint is completely flexible and more cost effective.
The present invention encompasses sensor assemblies incorporating various types of active sensing devices, including, but not limited to, magneto-resistive sensing devices and Hall-Effect sensing devices. Sensor assemblies incorporating passive sensing devices are also contemplated.
More specifically, the invention provides an electronic sensor assembly that can be used in various speed-sensing applications such as anti-lock brake systems. The sensor assembly includes a sensor element, a housing surrounding the sensor element, a terminal connected to the sensor element that extends outside of the housing for electrically coupling the sensor element to a conductor, a connector terminal for mechanically and electrically coupling the sensor terminal to the conductor, and a splice band mechanically and electrically coupling the sensor terminal to the connector terminal without welding, soldering, or using a crimp bucket. In one aspect of the invention, the sensor assembly further includes a capacitor electrically and mechanically coupled to the sensor terminal and the connector terminal via the splice band. The sensor element is preferably an active sensor such as a magneto-resistive sensor or a Hall-Effect sensor.
The invention also provides a method of assembling a sensor assembly having a sensor with at least two sensor terminals and a connector terminal having first and second legs. The method includes aligning a first sensor terminal and the first leg of the connector terminal, and splice-connecting the first sensor terminal and the first leg of the connector terminal to create a mechanical and electrical connection without welding, soldering, or using a crimp bucket. The method further includes aligning a second sensor terminal and the second leg of the connector terminal, and splice-connecting the second sensor terminal and the second leg of the connector terminal to create a mechanical and electrical connection without welding, soldering, or using a crimp bucket.
In one aspect of the invention, the sensor assembly further includes a capacitor having first and second capacitor terminals. The method further includes aligning the first capacitor terminal with the first sensor terminal and the first leg of the connector terminal, splice-connecting the first capacitor terminal with the first sensor terminal and the first leg of the connector terminal, aligning the second capacitor terminal with the second sensor terminal and the second leg of the connector terminal, and splice-connecting the second capacitor terminal with the second sensor terminal and the second leg of the connector terminal.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.